The present invention relates to a still picture communication system, in particular, relates to a hierarchy coding system of a still picture.
In a conventional facsimile system, a picture is encoded in a scanning manner so that each scanning line is encoded from top to bottom of a picture. In that system, almost all the coded data must be forwarded to a receive side, and therefore, it takes long time for transmission. When a picture data base is considered, that scanning system is unefficient in storing a picture, and/or retrieving a picture.
Another conventional system is a hierarchy encoding system, in which a bi-level image is progressively encoded beginning with a low resolution for a compressed image to subsequent doublings of resolution for an enlarged image.
In case of a dithering image which is conventionally used in printing or transmitting a picture, a multi-level image is first processed to be a dithered bi-level image, and the bi-level image is reduced to a low resolution image for hierarchy, and the each bi-level image is encoded starting from the lower resolution.
However, a prior hierarchy dithering encoding system has the disadvantage that a picture quality is poor in a low resolution image. That is because an image is first bi-leveled through dithering, and then, a dithered image is processed to hierarchy encoding by compressing the size of an image.